Surface reconstruction and transitions between different ordering with GaN thickness and growth rate as parameters. The growth was initiated on GaAs (001)-2x4. The maximum thickness for the transition indicates the border between nitrogen and gallium rich growth.
High-resolution SEM image of a GaN layer grown at N-rich conditions. Trenches can be seen on the surface, however, the area in between is smooth.
High-resolution SEM image of a GaN layer grown at N-rich conditions. Both the layer surface and the GaAs substrate are shown, where part of the layer has been peeled off.
High-resolution SEM image of a GaN sample grown at N-rich conditions. The surface of the GaAs substrate is shown, revealing polycrystalline structure with hollows, where the GaN layer has been peeled off.
High-resolution SEM image of a GaN layer grown at N-rich conditions. The smooth backside of the peeled-off GaN layer is shown, revealing homogeneously distributed and randomly shaped hexagonal crystallites, originating from the GaAs substrate.
High-resolution SEM image of a GaN layer grown under Ga-rich conditions. The excess Ga has formed droplets which are trapped in trenches.
High-resolution SEM image of a GaN layer grown under Ga-rich conditions. The removal of the Ga-droplets revealed nano-crystallites on the walls and edges of the trenches.
High-resolution SEM image of a GaN layer grown at near-stoichiometric conditions. The estimated surface roughness is ~20 nm, as determined by the nano-crystalline grains.
High-resolution SEM image of a GaN layer grown at near-stoichiometric conditions. It illustrates the columnar structure of small grains in the layer cross-section, while the surface part of the GaAs substrate shows neither indication of hollows, nor presence of polycrystalline structure.
AFM image of a GaN layer grown at near-stoichiometric conditions. The characterised area of 1 µm2 confirms the good surface roughness of ~20 nm or better, as was estimated by high-resolution SEM.
© 1998 The Materials Research Society
